I am currently renovating a small house and the kitchen is to be located at the front with the existing combined drain passing to the rear of the building. The kitchen will contain a sink, washing machine and dishwasher all connected to the same 40mm waste pipe (correct?). The distance between the combined drain to the nearest appliance is 4.3m.

Can I route this 40mm waste pipe below ground (within the floor slab) or must I use a 110mm drain to link between the existing combined drain and the kitchen?

I have to fit a trapped gully to the base of a RWP on the rear of the house which is close to the route of the kitchen waste. Could I connect this 40mm kitchen pipe into the gully below ground?

The combined drain is only 442mm below the depth of the proposed floor slab so achieving a good gradient relies on having a narrow diameter waste pipe. I am trying to avoid using a Saniflo unit if at all possible but this may be the only option if the above suggestion is out of the question.

IF YOU USE A 110mm PIPE, THE FALL REQUIRED OVER A 4M-5M DISTANCE AT 1:40 = 100mm-125mm.

KITCHEN WASTE CAN'T DRAIN INTO RAINWATER/SURFACE WATER ONLY GULLY.

YOU COULD INTRODUCE A NEW 110mm PIPE INTO THE MANHOLE/INSPECTION CHAMBER AND STRAIGHT ROUTE TO A TRAP POSITIONED BELOW GROUND OUTSIDE THE KITCHEN AND THEN PIPE FROM THE 3-LOCATIONS TO THE NEW TRAP USING YOUR 40mm PIPE WORK THROUGH WALL TO NEW TRAP.

I have examined your suggestion for running a 110mm drain under the new extension that will be located between the kitchen and the main drain and can see that I can achieve the gradient without any problems. This will include a large radius and a stub stack at the head which I can then tap my 40mm kitchen waste into through the wall.

I am surprised that you say that I cannot run the kitchen waste into a rainwater gully. Marley supply a product, the UG50 bottle gully, that has a 110mm back inlet to accept an underground drain to discharge into it before connection to the main drain/sewer and room in the grate above to accept a RWP. This would certainly simplify my drainage system and reduce the number of junctions into the main drain if it were possible.

Ok. Thanks. With regards to pipe sizes allowed underground, in general is it possible to have a smaller size (ie. 40mm) than 110mm fitted below ground (within solid floor)?

I also have to fit a new bathroom layout on the ground floor and would prefer the bath drainage to run underground to an exterior gully rather than having the waste pipe exit through the exterior wall and be visible on the rear of the building. The trouble with this is that the bath would be located on an existing ground floor slab and I would need to cut a hole in it to accept the waste pipe.

THE CONCERNS WITH SMALL DIAMETER PIPES BURIED IN A FLOOR SLAB ARE OF ACCESSABILITY IN THE EVENT OF A BLOCKAGE AND THEN THERE IS THE FROST PROBLEM AS TRAPS BURIED WITHIN A FLOOR AND BEING OF SMALL DIAMETER ARE PRONE TO FREEZING THE RESIDUAL WATER (CASE FOR INSULATION???).

THE PIPE SHOULD BE CONTINUOUS AND AS STRAIGHT/DIRECT AS POSSIBLE AT A CONSTANT FALL ANY JOINTS SOLVENT WELDED TO PREVENT JOINT MOVEMENT/DISCONNECTION OCCURING.
(BENDS AND LEVEL CHANGES = RISK OF BLOCKAGES/JOINT DISCONNECTIONS).

EXTENSIONS TO THE EXISTING EXTERNAL DRAINS ARE THE BETTER WAY TO GO IN MY HUMBLE OPINION, BROUGHT AS CLOSE TO THE POINT OF EXIT OF THE INTERNAL PIPEWORK WITH JUST A SHORT LENGTH AT THE INTERFACE/GULLY/TRAP.

YOUR LOCAL WATER AUTHORITY MIGHT HAVE RESTRICTIONS OR CODES OF PRACTICE TO COMPLY WITH FOR THE INSTALLATION YOU HAVE IN MIND AND IT WOULD BE WISE TO ATTAIN INFORMATION APPLICABLE TO YOUR LOCATION/SITUATION AND TO COMPLY WITH THE REGULATIONS.

DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!